Glycosylated hemoglobin level is associated with hearing impairment in older Japanese: The kurabuchi study

Objectives To examine the association between glycemic levels (glycosylated hemoglobin (HbA_1c)) and hearing impairment in a general older population. Design Community-based prospective longitudinal cohort study. Setting Kurabuchi Town, Gunma Prefecture, Japan. Participants Residents (N = 831; 350 men, 481 women) aged 65 and older were examined in 2005 and 2006 and analyzed in a cross-sectional study. Residents without hearing impairment at baseline who participated in audiometric re-examinations 4 years later were analyzed (n = 338). Measurements Hearing impairment was defined as failure to hear a 30-dB signal at 1 kHz and a 40-dB signal at 4 kHz in the better ear in pure-tone audiometric tests. Results Mean HbA_1c level (National Glycohemoglobin Standardization Program) was 5.8 ± 0.8% (40 mmol/mol). Odds ratios (ORs) and 95% confidence intervals (CIs) of hearing impairment associated with HbA_1c were estimated using a logistic regression model. In the cross-sectional analysis, HbA_1c levels were positively associated with hearing impairment (OR per 1.0% increase in HbA_1c = 1.30, 95% CI = 1.00-1.68). This association persisted even after excluding 58 participants with a self-reported history of diagnosed diabetes mellitus. Longitudinal analysis revealed the temporality of the discussed association (OR = 1.52, 95% CI = 1.03-2.23). Conclusion The present study provides supportive evidence for a causal link between hyperglycemia and age-related hearing loss.